Define the term "process variable".

The term "process variable" specifically refers to a variable that represents a measurable physical quantity within a system. This can include various parameters such as temperature, pressure, flow rate, and level, all of which are critical for monitoring and controlling industrial processes. By defining process variables accurately, operators can ensure that the system operates within its desired parameters, enhancing efficiency and safety.

This definition is crucial in the context of process control and instrumentation, as instruments are often employed to measure and regulate these variables to keep the process running smoothly. Understanding what constitutes a process variable allows for effective monitoring, control, and optimization of industrial operations.